Neutralizing Antibody Responses to Chlamydia trachomatis in Women and Associations With Chlamydia Outcomes

Abstract

We assessed neutralizing antibody responses in a well-characterized cohort of 60 women with different Chlamydia trachomatis infection outcomes noted at a treatment visit and 3-month follow-up. We found varying rates of neutralization (inhibition of C trachomatis) in sera at different dilution levels and varying neutralizing antibody titers across outcomes. Median neutralization rates were significantly higher in sera at high dilutions (1:320-1:1280) from women with spontaneous resolution vs persisting infection before treatment (all P < .05). These findings suggest that neutralizing antibody responses may contribute to protective immunity against chlamydia.

Keywords: chlamydia infection; clinical outcomes; neutralizing antibody; serology; women.

Figure 1.

Chlamydia trachomatis neutralizing antibody responses in women presenting for treatment of chlamydia and in women who were C trachomatis naive. A comparison was made between neutralizing antibodies against C trachomatis serovar D elementary bodies (EBs) in 60 serum samples at the enrollment visit from 60 women presenting for treatment of chlamydia (treated) and in 20 serum samples from 20 women who were C trachomatis naive (naive). A, Percentage inhibition of infection (neutralization rate) in serum samples with a 1:10 dilution. B, Neutralization half-maximal inhibitory concentration (IC50) of serum samples. A and B, Percentage inhibition of infection and neutralization IC50 were significantly higher in women treated for chlamydia vs women who were C trachomatis naive. Statistical significance was analyzed by Mann-Whitney test. Horizontal bar represents the median.

Figure 2.

Chlamydia trachomatis neutralizing antibody titers across enrollment and 3-month follow-up visits and association of neutralizing antibody responses with different chlamydia outcomes. A, Mean neutralization half-maximal inhibitory concentration (IC50) values at an enrollment visit (V1) vs 3-month follow-up visit (V2) in women: all treated (N = 60), reinfected (n = 20), and not reinfected (n = 40). B, Median neutralization IC50 values of serum from groups with different chlamydia outcomes at V1 and V2: spontaneous resolved (n = 20) vs persisting infection (n = 40) at V1 and presence of reinfection (n = 20) vs no reinfection (n = 20) at V2 stratified by persistent infection status at V1. Resolved_V1 refers to the spontaneous resolution of chlamydia before treatment at V1, and all women in this group had no reinfection at V2 (Resolved_V2). C, Median percentage inhibition of infection of C trachomatis serovar D elementary bodies in V1 serum samples with different dilutions. A, There was a trend toward a decline in mean neutralization IC50 from V1 to V2, which was driven by a significant decline in those without reinfection. B, Median neutralization IC50 was not significantly associated with chlamydia outcomes. C, Medians of percentage inhibition of infection were significantly higher in those with spontaneous resolution vs persisting infection at V1 at serum dilutions of 1:320 or higher but not at lower serum dilutions. Statistical significance was analyzed by (A) a paired t test and (B and C) a Mann-Whitney test.